I would reference the behavioral economics on loss aversion to up the value of a task. Rather than focusing on increasing the positive value via upping the reward, I would increase the negative value of inaction. Personally, I've taken to fining myself for not getting things done on time (all the money goes into a jar next to my desk, which goes to charity at the end of the month). This system has worked wonders - it even has power to control my less rational selves (e.g. drunk self and just-woke-up self)